An internal mixer of the kind described above is known from German Pat. No. 541,788. In this case the mixing shafts are so shaped that, viewed in the longitudinal direction of the mixing shafts, the kneading blades are disposed in the middle of the mixing shafts, and the roller surfaces, which are in the form of narrow cylinders, are disposed in the region of the front ends of the mixing shafts. The mixing shafts rotate with different peripheral speeds of the roller surfaces or of the radially external surfaces of the kneading blades. The kneading blades are disposed at an angle to the longitudinal axis of the mixing shafts with the tip of the angle leading in the direction of rotation. In this way it is intended to ensure that the material being processed will come into the gap between the roller surfaces. On their sides which trails in the direction of rotation the kneading blades have an angular shape with the tip of the angle trailing in the direction of rotation. In this way it is intended to ensure that the material will be removed from the roller surface again and brought into the region of the kneading blades.
In this known internal mixer it has thus already been attempted to combine, on the one hand, the advantages of pure roller mixers, namely uniform and constrained homogenization of the entire mixture in the roller gap, working with a thin layer in the roller gap, and working with a low temperature level, and on the other hand, the advantages of internal mixers working only with kneading blades, that is to say the application of a large amount of energy per unit of time and consequently short mixing times, the simultaneous application of energy to the entire material being mixed, low atmospheric pollution because of the closed construction, a high degree of filing, and ease of operation. This attempt failed because it was not possible to ensure that the entire mixture would be uniformly taken up by the kneading blades and the roller surfaces, because the direction of flow for transferring the material being mixed from the kneading blade to the roller surfaces must be in the direction of the axis, that is to say at right angles to the rotation of the blades.
From German Pat. No. 646,308 (corresponding to British Pat. No. 431,012), an internal mixer is moreover known which has intermeshing kneading rollers and in which mutually offset roller surfaces were disposed on the periphery of each of the mixing shafts, these roller surfaces engaging in one another when the mixing shafts, which rotate in opposite directions and with the same peripheral speed, roll over one another. Through this mutual engagement of the kneading rollers, the roller gap was lengthened and thus the volume of rotating material being mixed was increased. In this known mixer, as also in a rolling mill, temperatures can be effectively controlled. In this known internal mixer, however, the mixing action was found to be unsatisfactory.
The problem sought to be resolved by the present invention is that of improving an internal mixer of the kind first described above, in such a manner that the exchange of material being mixed between the kneading blades and the roller gap is effected between the roller surfaces by constraint and completely uniformly for the entire material being mixed.